Typical engines have an exhaust system that include a filtration process for filtering particulates out of the exhaust stream so that the emissions exiting the exhaust system comply with regional environmental regulations and/or worldwide environmental regulations. These environmental standards and regulations are becoming stricter and require that the amount of Nitrogen Oxide (NOx), Hydrocarbon (HC), and Carbon Monoxide (CO) exiting the exhaust system are reduced in order to meet the standards set forth in the regulations. Additional emissions abatement components such as Selective Catalyst Reduction (SCR), Diesel Oxidation Catalysts (DOC), NOx Absorbing Catalyst (NAC), Lean NOx Trap (LNT), or a combination thereof may be required in the exhaust system so that the exhaust can be further cleaned (e.g. removal of NOx from the exhaust stream). The tightening of emission standards has required that more contaminates are removed from the exhaust stream. The addition of one or more of these components has reduced the amount of space available in the exhaust system. As exhaust components are added the overall fuel consumption is increased and there is a need to improve the overall fuel consumption and/or improve fuel economy. For example, one to three percent of the total fuel consumed is utilized performing regeneration cycles.
Regeneration of the particulate filters is performed when the particulate filters reach a target soot loading and/or it becomes increasingly difficult for the exhaust to pass through the particulate filter. Currently, there is no accurate way to calculate the actual soot load (i.e., target soot load) of a particulate filter; thus, regeneration cycles are triggered based upon fuel consumption, vehicle mileage, engine running time, and engine emission rates. Attempts have been made to trigger regeneration cycles based upon soot loading; however, the current particulate filters and particulate filter system have a relatively high variability in calculating the target soot load. Thus, the regeneration cycle is begun when the target soot load is achieved; however, the other process variables are set using the calculated maximum soot load so that the diesel particulate filter is not damaged. The maximum soot load for triggering a regeneration cycle may be calculated by taking the target soot load plus the variability in calculating a soot load. For example, the maximum soot load may be calculated by taking a target soot load of 5 grams/liter and adding the variability in calculating the soot load of ±2 grams/liter. Therefore, under this system the regeneration cycle will begin when the target soot load is 5 grams/liter. However, due to the variability in calculating the maximum soot loading the particulate filter may actually contain between about 3 grams/liter to about 7 grams/liter. Thus, due to the variability in calculating the target soot load of the particulate filters the inlet gas temperature may be set for the maximum soot load, which may result in increased regeneration times, higher or lower temperatures than the target temperatures, inconsistent efficiency from regeneration to regeneration, low regeneration efficiency, the regeneration cycle occurring below and/or above the target soot load, or a combination thereof.
Another challenge faced during regeneration of a particulate filter is maximizing the regeneration temperature without creating a “runaway” reaction or exceeding a temperature of about 800° C. so that exhaust system components are not damaged. Temperatures greater than about 1000° C. may cause the particulate filter to crack, melt, deactivate or reduce the efficiency of a catalyst coating on the particulate filter, or a combination thereof. If the particulate filter cracks, melts, or the catalyst coating is deactivated compliance with environmental regulations (e.g. regulations by the Environmental Protection Agency (EPA)) may not be met.
Currently, if a regeneration cycle is in progress and the engine speed is reduced to an idle, the temperature of the exhaust system drastically increases due to the reduced exhaust flow through the exhaust system and particularly the temperature of the particulate filter drastically increases. Attempts have been made to decrease the filter temperature by maintaining a high engine speed at idle so that a high air flow through the particulate filter is maintained. However, maintaining the engine at a higher speed during idle presents other challenges such as engine noise, emissions, and may also result in a fuel penalty. Some attempts to control the temperature of a diesel particulate filter during a regeneration cycle can be found in U.S. Pat. No. 7,275,365; and U.S. Patent Application Publication Nos. 2007/0193258; 2008/0016856; and 2009/0241512, incorporated by reference herein for all purposes. What is needed is a particulate filter and particulate filter control system that requires less packing space, reduces fuel consumption, increases the regeneration temperature, shortens the regeneration duration, improves regeneration efficiency, a reduced system cost for the exhaust system, or a combination thereof without causing a runaway reaction or damaging the components of the exhaust system.